Colour picture tubes containing an in-line type electron gun assemblies

ABSTRACT

In an in-line type colour picture tube provided with dynamic and static convergences there is provided a pole piece assembly disposed in the plane of convergence adjustment. The pole piece assembly comprises first and second pairs of pole piece segments which are disposed substantially at right angles with each other. The second pair of pole piece segments is disposed in a direction coinciding with the direction of vertical deflection of the electron beams.

United States Patent Yamauchi Aug. 12, 1975 [54] COLOUR PICTURE TUBES CQNTAINING 3,325,675 6/1967 Sanford 313/412 X AN INJJNE TYPE ELECTRON GUN 3,840,765 10/ 1974 Takenaka 313/428 ASSEMBLIES R27,75l 9/1973 Yoshida et al 313/412 X [75] Inventor: Masaaki Yamauchi, Mobara, Japan primary i mg Harris [73] Assignee; Hitachi, Ltd Tokyo Japan Attorney, Ageiit; 0r FirmCharles E. Pfund, Esq.

22 Filed: Feb. 21, 1974 Appl. No.1 444,275

Foreign Application PriorityData, May 4. 1973 Japan ..48-491 12 US. Cl 335/211; 313/428 Int. Cl. HOIF 3/12 Field of Search 335/210; 313/412, 421, 313/425, 426, 427, 428

References Cited UNITED STATES PATENTS 2/1960 Gundert 313/412 [5 7] ABSTRACT In an in-line type colour picture tube provided with dynamic and static convergences there is provided a pole piece assembly disposed in the plane of convergence adjustment. The pole piece assembly comprises first and second pairs of pole piece segments which are disposed silbstantially at right angles with each other. The second pair of pole piece segments is disposed in a direction coinciding with the direction of vertical deflection of the electron beams.

2 Claims, 8 Drawing Figures PATENTED AUB 1 21975 SHEET F/GLZ PATENTEB AUG 1 2 I975 SHEET FIG] (BJLG COLOUR PICTURE TUBES CONTAINING AN IN-LINE TYPE ELECTRON GUN ASSEMBLIES BACKGROUND OF THE INVENTION This invention relates to a colour picture tube con taining an in-line type electron gun assembly (hereinafter, merely termed an in-line type colour picture tube), more particularly to an improved construction of the convergence pole pieces for readily effecting a dynamic convergence by utilizing the deflection magnetic field at the rear end of a deflection yoke which is utilized to scan the electron beams.

In the in-line type colour picture tube wherein no field correction by pole pieces is provided, the tasters of three electron beams .do not generally coincide with each other in the vertical and horizontal peripheries of the fluorescent screen. Especially, the deflection sensitivity of the electron beam emanated from the central electron gun to the vertical deflection field is smaller than that of the electron beams emanated from the electron guns on both sides. Such a phenomenon is caused by the characteristic of the deflection yoke.

Under these conditions, it is necessary to apply the dynamic convergence by an external circuit both in the horizontal and vertical directions.

To apply a static convergence to an in-line type colour picture tube it has been the practice to hold stationary the electron beam emanated by the central electron gun by means of a magnetic shield, to shift the electron beams emanated from the side electron guns by the magnetic field generated by a magnet utilized for providing the static convergence, thereby causing the central electron beam to coincide with the electron beams emanated by the electron guns on both sides. Actually, however, as it is necessary to make short, as faras possible, the total length of the colour picture tube the field of the magnet for providing the static convergence and the deflection field at the rear endof the deflection yoke overlap with each other. For this reason, shielding of the electron beam of the central electron gun from the field for the static convergence also shields a portion of the vertical and horizontal deflection fields with the result that the raster of the central electric field will be shifted toward the center of the fluorescent screen. In other words, the deflection sensitivity of the electron beam from the central electron gun is decreased relative to the case wherein the electron beam is not magnetically shielded both in the horizontal and vertical directions. If the dynamic convergence were to be applied under these conditions it would be necessary to supply a current having an asymmetrical waveform with respect to the direction of the horizontal deflection of the electron beams emanated from the electron guns on both sides. Further, it is necessary to provide a complicated dynamic convergence circuit which increases the deflection sensitivity of the electron beam from the central electron gun for the vertical deflection or decreases the deflection sensitivity of the electron beams emanated from the electron guns on both sides.

To solve these problems the applicant has proposed an improved construction as disclosed in Japanese patent application No. 10941 1/1972, filed on Nov. 2, 1972. According to this proposed construction two ar cuate pole pieces with their opposite ends flared outwardly are provided at a position near the front end of three electron guns arranged in-line on the opposite sides of the central electron gun and in a substantially horizontal direction which is perpendicular to the axis of the colour picture tube. Further, another pole piece having substantially the same configuration as the first mentioned pole pieces is disposed above the electron guns on the opposite sides symmetrically with one of the first mentioned pole pieces. With this construction, the vertical deflection field applied to the electron beams from the electron guns on both sides near the pole pieces can be decreased relative to that of the case wherein no pole piece is used and the vertical deflection field applied to the electron beam from the central electron gun can be increased relative to that of the case wherein no pole piece is used thereby compensating for the difference in the vertical deflection sensitivity and eliminating the difference in the horizontal deflection sensitivity caused by the magnetic shield.

However, even with this improved construction it is impossible to sufficiently compensate for the differences in the vertical and horizontal deflection sensitivities. Further since, the pole pieces positioned at the outer ends of the electron guns on both sides intercept the horizontal dynamic convergence field for the'electron beams emanated by the electron guns on both sides, it is not only impossible to apply satisfactory convergence but also increases the electric power consumed by the external convergence circuit. Moreover, the construction of the fixtures for holding the pole pieces is complicated and bulky, thus requiring a large space.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved in-line type colour picture tube in which the static and dynamic convergences can be provided on the same plane and the dynamic convergence can be adjusted readily.

Another object of this invention is to provide an improved in-line type colour picture tube including a convergence pole piece assembly capable of eliminating the compensation for the dynamic convergence for the vertical deflection and which permits use of currentof a symmetrical waveform for the dynamic convergence in the horizontal direction for the electron beams from the electron guns on the opposite sides.

Still another object of this invention is to provide an in-line type colour picture tube provided with convergence pole pieces of the improved construction which do not intercept the fields of the static and dynamic convergences for the electron beams emanating from. the electron guns on both sides. 7

Yet another object of this invention is to provide an in-line type colour picture tube having convergence pole pieces which are simple in construction and can be mounted readily.

In accordance with this invention, these and further objects can be accomplished by providing an in-line type colour picture tube of the type comprising three electron guns arranged on a straight line, and means for adjusting on substantially the same plane the dynamic convergence and the static convergence provided for concentrating three electron beams emanated from the three electron guns at a point on the fluorescent screen of the colour picture tube, characterized in that there is provided a pole piece assembly disposed in said plane of convergence adjustment, that the pole piece assembly includes a first pair of pole piece segments and a second pair of pole piece segments, that the pairs are disposed substantially at right angles with each other, and that the first pair of pole piece segments is disposed in a direction coinciding with the direction of vertical deflection of the electron beams.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a portion of an in-line type colour picture tube;

FIG. 2 is a diagram showing typical rasters where no pole piece is used;

FIG. 3 is a diagram showing typical rasters where the central electron gun is magnetically shielded;

FIG. 4 is a perspective view of one example of the pole pieces embodying the invention;

FIG. 5 is a cross-sectional view of the assembly of the pole pieces shown in FIG. 4;

FIG. 6 is a diagram to explain the operation of this invention;

FIG. 7 is a diagram showing the rasters appearing in the colour picture tube embodying the invention; and

FIG. 8 is a diagrammatic representation to explain the operation of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 which shows the construction of the deflector of an in-line type colour picture tube, electron beams B B and B emanated from electron guns G G and B respectively are corrected by a convergence adjusting member 1 and are then deflected by a deflection yoke 2 so as to scan the entire surface of a fluorescent screen (not shown) of the colour picture tube. It is to be understood that the convergence member 1 includes a dynamic convergence adjuster and a static convergence adjuster which are arranged on the same plane. Since the convergence adjusting member 1 and the deflection yoke 2 are located close to each other the pole pieces (not shown) for field correction which are disposed on substantially the same plane as the convergence adjusting member 1 are subjected to the complicated action of the flux produced by the deflection yoke 2, and the fluxes for providing the dynamic and static convergences. Especially at the time of adjusting the static convergence, if one tries to coincide the electron beam B B or B on one side with the central electron beam B,,, the central electron beam B will be moved by the interference with the flux for effecting the static convergence thus rendering it difficult to adjust.

FIG'. 2 shows a manner of misconvergence of the electron beams B, G and R for respective colours at the periphery of the fluorescent screen where no pole piece for field correction is used, such manner representing the characteristic of the deflection yoke. As shown in this figure, in the vertical direction the deflection of the red beam R is not sufficient so that the red beam R is positioned on the inside of the screen with respect to the blue beam B and the green beam G. In the horizontal direction, the red beam R is positioned between the blue beam B and the green beam G. With the conditions of the rasters of the electron beams as' shown in FIG. 2 if a'magnetic shield were provided as shown by dotted lines in FIG. 3 for the purpose of avoiding the interference caused by the static convergence flux of the central electron gun G the interferences caused by the electron guns G and G would be decreased thus making it easy to adjust. But as shown by the rasters on the fluorescent screen shown in FIG. 3, at the periphery of the screen, the raster of the red beam R will be shifted toward the center of the screen thus making it difficult to make convergence with other beams B and G.

One embodiment of this invention will now be described with reference to FIGS. 4 and 5. The pole piece assembly of this invention for correcting the magnetic field comprises a first pair of pole piece segments 3 and a second pair of pole piece segments 6. Each pole piece segment 3 is outwardly concave and includes a central fiat portion 3a and inclined portions 3b on both sides thereof. Each pole piece segment 6 comprises an arcuate portion 6a and a flat web 6b extending in the diametrical direction from the center of the arcuate por tion 6a. Pole piece segments 3 and 6 are made of a material of high permeability, for example permalloy, for providing magnetic paths of low reluctance. Accordingly, it is necessary to form portions 3a and 3b and 6a and 6b as integral structures not including any air gap or other region of high reluctance at the interface between these parts.

As shown in FIG. 5, two pole piece segments 3 are disposed symmetrically with their back surfaces opposed to each other and are secured to the inside of a cylindrical cage 5 by means of supporting members 4. The supporting members 4 and the cylindrical cage 5 are required to be made of a material that transmits magnetic flux, non-magnetic stainless steel for example. The pole piece segments 6 are disposed between the spaced pair of segments 3 with their arcuate portions 6a secured to the inside of the cylindrical cage 5. The pairs of segments 3 and 6 are combined to form an assembly wherein a line interconnecting the webs 6b of the segments 6 intersects at right angles with a line interconnecting the centers of the segments 3. Since the pole piece assembly is disposed on the convergence adjusting surface of the colour picture tube such that the pair of segments 3 coincides with the direction of the vertical deflection, the central electron beam R will pass through the center of a space bounded by the segments 3 and 6 whereas the electron beams B and G will pass through the spaces defined by the left and right segments 3 and the cylindrical cage 5.

When the pole piece assembly described above is disposed in the deflection magnetic field, a distribution of the magnetic flux as shown in FIG. 6 is obtained. More particularly, the pole piece segments 3 function to gather the vertical deflection flux VH at the center to increase the vertical deflection sensitivity of the central electron beam, that is the red beam R. This is caused by the fact that a magnetic path having a small relucthe deflection of three electron beams in the horizontal direction will be substantially the same as that of the case wherein no pole is provided.

Consequently, it will be understood that by using the pole piece segments of this invention, it is possible to obtain rasters as shown in FIG. 7 instead of those shown in FIGS. 2 and 3. FIG. 7 shows a condition wherein the left and right hand rasters are maintained unchanged but the rasters R along the upper and lower edges are made to coincide with the rasters B and G on the same sides. As it is possible to obtain rasters as shown in FIG. 7, in the in-line type colour picture tube embodying the invention, it is not necessary to provide a vertical dynamic convergence. Moreover, it is possible to provide a horizontal dynamic convergence for the blue and green beams with respect to the red beam R by using a current having symmetrical waveform.

Two pairs of pole piece segments 3 and 6 provide the function of the magnetic shield that prevents the flux of an external adjusting member, not shown, from interferring with the central electron beam (red beam R). This function will be described with reference to FIG. 8.

FIG. 8 shows the relationship between the static and dynamic convergences and the pole piece sections embodying the invention, in which the lefthand side a shows the function of the dynamic convergence, whereas the righthand side b that of the static convergence. As shown, the static convergence is provided by rotating magnets M M M and M for adjusting the polarity and intensity of the flux SH flowing through E shaped magnetic cores of the convergence adjusting member 1 so as to statically coincide the outside beams (green and blue beams B and B with the central beam B The dynamic convergence is provided by passing a current having a parabolic waveform through a coil 8 of the convergence adjusting member 1 from an external source E.C.S. to form the dynamic convergence flux D which shifts the blue and green electron beams B and B to coincide with the central red beam B In this manner, as the external fluxes D and S do not interfere with the central beam 8,, to any appreciable extent it is possible to readily adjust the convergence. In addition, since the convergence field for the electron beams on both sides is not shielded, the power required for the dynamic convergence may be small. It is necessary to vary the size and configuration of the two pairs of pole piece segments 3 and 6 in accordance with the flux distribution of the external convergence field and the flux distribution of the deflection yoke.

The correction of the convergence provided by this invention is most suitable for the convergence of the simple type such as those utilizing saddle type deflection yoke or of the wide angle (110) deflection type.

As has been described in detail, when the pole piece segments of this invention are used, even in the inline type colour picture tube in which the dynamic and static convergences are provided in the same plane, a pair of pole piece segments 3 acts to increase the deflection of the central beam (red beam B in the vertical direction and the other pair of the pole piece segments 6 functions to cause the horizontal deflection flux to act uniformly upon respective electron beams. Moreover as it is possible to prevent the fluxes of the dynamic and static convergences from interferring with the central electron beam it is possible to readily adjust the convergence of the colour picture tube.

Thus, the invention provides an improved colour picture tube in which the adjustment of the convergence can be readily made in a short time even by a unskilled person.

What is claimed is:

1. In an in-line type colour picture tube of the type comprising three electron guns arranged on a straight line, and means for adjusting on substantially the same plane the dynamic convergence and the static convergence provided for concentrating three electron beams emanated from said three electron guns at a point on the fluorescent screen of said colour picture tube, the improvement which comprises a pole piece assembly disposed in said plane of convergence adjustment, said pole piece assembly including a first pair of spaced pole piece segments substantially symmetrically disposed with respect to a plane perpendicular to said straight line, which plane passes through the axis of a central electron gun, one of said first paired pole piece segments being disposed between the axes of the central electron gun and an outer electron gun, the other being disposed between the axes of the central electron gun and the other outer electron gun, individual segments of said first paired pole piece segments being disposed also symmetrically with respect to another plane passing through the axes of the three electron guns and opposed to each other by a smaller distance at said straight line than at the extremities remote from said straight line, and a second pair of pole piece segments being disposed symmetrically with respect to said plane passing through the axes of three electron guns, individual segments of said second paired pole piece segments being disposed also substantially symmetrically with respect to said plane perpendicular to said straight line and passing through the axis of the central electron gun, and having a web projecting toward said central electron gun substantially on the last mentioned plane.

2. The colour picture tube according to claim 1 wherein said two pairs of pole piece segments and said webs are made of a material of high permeability and mounted in a cylindrical cage made of a magnetic flux transmissible material. 

1. In an in-line type colour picture tube of the type comprising three electron guns arranged on a straight line, and means for adjusting on substantially the same plane the dynamic convergence and the static convergence provided for concentrating three electron beams emanated from said three electron guns at a point on the fluorescent screen of said colour picture tube, the improvement which comprises a pole piece assembly disposed in said plane of convergence adjustment, said pole piece assembly including a first pair of spaced pole piece segments substantially symmetrically disposed with respect to a plane perpendicular to said straight line, which plane passes through the axis of a central electron gun, one of said first paired pole piece segments being disposed between the axes of the central electron gun and an outer electron gun, the other being disposed between the axes of the central electron gun and the other outer electron gun, individual segments of said first paired pole piece segments being disposed also symmetrically with respect to another plane passing through the axes of the three electron guns and opposed to each other by a smaller distance at said straight line than at the extremities remote from said straight line, and a second pair of pole piece segments being disposed symmetricalLy with respect to said plane passing through the axes of three electron guns, individual segments of said second paired pole piece segments being disposed also substantially symmetrically with respect to said plane perpendicular to said straight line and passing through the axis of the central electron gun, and having a web projecting toward said central electron gun substantially on the last mentioned plane.
 2. The colour picture tube according to claim 1 wherein said two pairs of pole piece segments and said webs are made of a material of high permeability and mounted in a cylindrical cage made of a magnetic flux transmissible material. 